Production of magnesium utilizing a tubular condenser



July 14, 1970 Filed Oct. 17. 1967 CALCINING ZONE E. A. STAWARZ ET AL 3,520,524

PRODUCTION OF MAGNESIUM UTILIZING A TUBULAR CONDENSER1 2 Sheets-.Sheet l BY fwjylciewv PATENT ATTORNEY July 14, 1970 E. A. STAWARZ ET AL PRODUCTION OF MAGNESIUM UTILIZING A TUBULAR CONDENSER Filed Oct. 17. 1967 FIGURE 2 2 Sheets-Sheet 2 INVENTORS msmws @MMM/M2M Y fw. (2

PATENT ATTORNEY United States Patent O 3,520,524 PRODUCTION OF MAGNESIUM UTILIZING A TUBULAR CONDENSER Edmund A. Stawarz, Morristown, Robert W. Schnepf, Berkeley Heights, Benjamin Eisenberg, Parsippany, and Richard P. Rhodes, Roselle, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Oct. 17, 1967, Ser. No. 675,973 Int. Cl. C22b 45/00; F27d 1/12 U.S. Cl. 266--34 4 Claims ABSTRACT OF THE DISCLOSURE A thermal apparatus for the production of magnesium metal at substantially atmospheric pressure which comprises heating an alloy mixture in a reaction zone at a temperature in the range from about 2850" to 3100 F., removing a gaseous mixture of hydrogen and magnesium vapor from the reaction zone and thereafter utilizing a tubular condenser to remove and recover the magnesium as a liquid.

The present invention is broadly concerned with the production of high quality magnesium metal utilizing a thermal technique. The invention is especially concerned with the thermal treatment of a feed mixture of dolomite (CaO-MgO) and aluminum silicon (AlzSi) utilizing an apparatus and other feed reactants wherein magnesium vapor is continuously produced. The magnesium is recovered from a gaseous mixture of magnesium and hydrogen or other inert gas `by the utilization of a unique tubular condenser.

It is known in the art that the present thermal methods for the production of magnesium are slow batch operations wherein a high vacuum is required. These known thermal methods thus are not suitable for operations on a scale large enough to compete with the electrolytic cell methods for the production of magnesium. The present invention is based upon the discovery that magnesium vapor may be readily distilled and recovered and that a ferrosilicon by-product may be simultaneously produced without the use of vacuum providing thereactants and the reaction Zone conditions are controlled within critical limits. In accordance with one specific adaptation of the present invention, aluminum-silicon-iron alloy is reacted with a critical mixture of calcium oxide and magnesium oxide under temperature and pressure conditions in an integrated process to produce high quality magnesium vapor and a molten slag. Hydrogen or other inert gases may also be introduced into the reaction zone and the magnesium thereafter recovered from the gaseous mixture by the utilization of a particularly designed tubular condenser.

The tubular condenser technique of the present invention may be utilized for the recovery of magnesium from a magnesium-containing vapor mixture when using Wide ranges of reactants and reaction conditions in the reduction zone. However, the invention will be described utilizing particular reactants and operating conditions and may be fully understood by reference to the drawings illustrating one preferred embodiment of the same.

Referring specifically to FIG. 1, a mixture of aluminum oxide, iron oxide and silicon oxide is introduced into ICC alloy furnace 10 by means of line 1. Alloy furnace 10 may comprise any suitable furnace such as a conventional electric arc furnace. The required carbon is introduced into furnace 10 by means of line 2. Gaseous reaction products are removed from furnace 10 by means of line 3 while an aluminum-silicon-iron alloy is removed from furnace 10 by means of line 5. The temperature in furnace 10 is maintained in the range from about 3200 F. to 00 F., preferably about 4000" F. The pressure in alloy furnace 10 is in the range from about 0.5 to 2 atmospheres preferably about 0.9 to 1.1 atmospheres such as about 1.0 atmosphere.

The feed reactants added to furnace 10 are preferably added in amounts so as to produce an alloy comprising about 40 to 90% by weight of aluminum, about 65 to 10% by weight of silicon and about l to 20% by weight of iron. A preferred alloy consists of about by weight of the aluminum, about 40% by weight of silicon and about 10% by weight of iron. Satisfactory reactants for feed to alloy furnace 10 are clay, bauxite, iron oxide and carbon.

The alloy removed from zone 10 by means of line 5 comprising aluminum, silicon, and iron may be passed directly in the molten state to reducing furnace 40. This alloy, however, may be passed by means of line 6 into a cooling and crushing zone 30 and thereafter mixed with the reaction mixture of Calcined dolomite and magnesia which is introduced into the system by means of line 8.

Calcined dolomite is produced by introducing dolomite (calcium carbonate and magnesium carbonate) into calcining zone 20 by means of line 9. The calcined dolomite produced in Zone 20 and withdrawn by means of line 8, comprises about to 65% by weight of calcium oxide and about 45 to 35% by weight of magnesium oxide. Magnesia, which is substantially pure magnesium oxide (greater than about 90%), is introduced with the dolomite by means of line 11. The amount of magnesia added by means of line 11 is such as to secure a MgO/CaO ratio in the oxide mixture fed to the reaction zone in the range of about 50/ 50 to 80/20 parts by weight, preferably from about 55/45 to 65/35 and, more particularly, about /40 parts by weight. Alternatively, a Calcined magnesitic dolomite of the proper CaO/MgO ratio could be fed directly into line 8.

If the alloy is passed to Zone 30 it is withdrawn by means of line 13 mixed with the magnesia-calcium-oxide mixture and introduced into reaction furnace 40. On the other hand, if the alloy is introduced directly into reaction Zone 40, the magnesia-calcium-oxide mixture is introduced by means of line 13. A preferred adaptation is to introduce about 40 to 60%, such as about 50%, of the alloy directly into zone 40 by means of line 5 and to introduce the remainder mixed with the magnesium-calcium-oxide by means of line 13.

The amount of the mixture of Calcined dolomite and magnesia introduced into furnace zone 40 as compared with the amount of aluminum-silicon-iron alloy introduced into furnace zone 40 is in the range of from about 3.0 to 8.0 parts by weight per 1.0 part by weight of alloy. A preferred ratio of the mixed oxides-to-alloy is in the range of from about 4.0 to 1.0 by weight.

Reduction furnace 40 is maintained at a pressure in the range from 0.5 to 2.0 atmospheres, preferably 0.9 to 1.1 such as about 1 atmosphere. Under one preferred method of operation, the temperature in reduction furnace 40 is maintained in the range from about 2850 F, to 3100 F., preferably about 2950 F. The slag phase 41 in reduction furnace 40 comprises aluminum oxide, calcium oxide and silicon oxide. When the reactants are introduced into slag phase 41, they melt and form discrete particles of alloy in slag phase 41. These discrete particles are a homogeneous metal phase of aluminum, silicon and iron.

Under these conditions the aluminum reacts with calcium oxide to form aluminum oxide in the slag and the calcium replaces the aluminum in the discrete particles of the metal phase. This latter metal phase of iron, silicon and calcium will separate, if the slag density is suflicient, to yield an upper metal phase 42. Hydrogen is introduced into the vaporous area of reduction furnace 40 by means of line 43. The calcium reacts with the magnesium oxide to form calcium oxide which is segregated in the slag 41 and vaporous magnesium is formed which is removed from reduction furnace 40 along with the hydrogen by means of tubular condenser 50 and recovered as hereinafter described.

Due to the fact that a portion of the calcium in phase 42 is removed by reacting with the magnesium oxide, the density of the alloy increases and a lower phase of iron. and silicon 44 forms at the bottom of reaction zone 40. Thus, a ferrosilicon phase 44 comprising from about 30-80% silicon and 70-20% iron may be withdrawn from zone 40 by means of line 45 and utilized as desired in the steel industry. The slag is removed from reduction furnace 40 by means of line 46 and handled as desired while a ferrosilicon-calcium phase may be withdrawn by means of line 47 and further handled to segregate the respective elements.

Sufficient hydrogen is introduced into the vaporous area of furnace 40 so as to maintain the pressure at about atmospheric pressure as, for example, in the range from about 0.5 to 2.0 atmospheres. In general, the vaporous mixture withdrawn by means of condenser 50 comprises about 90 to 40 volume percent of magnesium and from about to 60% of hydrogen.

The temperature of the vaporous mixture entering tubular condenser 50 is in the range of from about 2000 F. to 3100 F. usually about 2600 F. As the vaporous mixture passes downwardly through tubular condenser 50 the temperature is reduced to within the range of from about 1200 F. to 1500 F., usually about l250 F. Liquid magnesium collects in collecting zone 54 and is Withdrawn by means of line 55. Hydrogen is removed from zone 54 by means of line 43 and recycled to reduction furnace 40.

Tubular condenser 50 comprises a single long cylindrical metal shell 60 with an internal lining 51 such as carbon or graphite whose thickness is selected to keep the shell temperature within allowable limits. Thus, direct condensation of hot metal vapors onto a bare metal surface is avoided. High heat transfer rates are achieved either by operating with a cold shell and utilizing water as a coolant which is sprayed around the periphery of the shell by means of suitable spray elements 52 and 53. Any number or arrangement of water spray elements may be utilized. On the other hand, the shell may be operated with a hot shell and radiating the heat to the atmosphere.

A unique feature of the present invention is that liner 51 has a relatively high heat transfer rate where the metallic vapors are condensing near the top of the unit. The liner 51 at the lower end of the condenser has a relatively low heat transfer rate. This progressive change in heat transfer rate from relatively high to relatively low of liner 51 may be achieved by any suitable means. One method will be clearly described with respect to FIG. 2.

A preferred and very satisfactory condenser in accordance with the present invention is illustrated in FIG. 2 wherein upow of the vapors is secured. The condenser is so designed that the internal temperature of the lining along its entire length is above the freezing point of the magnesium which is secured by having a lining of very high conductivity in the lower area of the condenser which lining is adjusted so that the conductivity of the lining decreases as the vapors flow upwardly through the condenser. Here again, the relatively high heat transfer rate for the liner is at the lower end of the condenser wherein the metallic vapors are condensing. Condenser 70 comprises a carbon steel shell 71 which is internally lined in a particular manner with courses of carbon and graphite. The vapors are removed from the furnace and introduced into condenser 70 by means of line 72. Magnesium is condensed and is collected in area 54 and withdrawn from the system by means of line 55. Water sprays 52 and 53 are utilized to maintain the desired temperature on the condenser exterior. Uncondensed hydrogen is withdrawn by means of line 43 and recycled as described in FIG. 1.

In order to achieve the desired results as described the diameter of condenser 70 may be from about 5 feet to 8 feet as, for example, about 6 feet. The length of the condenser is from about -120 feet, such as about 100 feet. The interior of the condenser as, for example in area 58, is lined with graphite bricks as, for example, with nine courses of 2inch graphite bricks for a total thickness of about 18 inches. The lining in the upper part of the condenser contains progressively more carbon bricks having lower conductivity. For example, the lining in area 59 consists of about eight courses of 2inch carbon bricks and one course of 2inch graphite bricks. The lining at the top of the condenser would consist of nine courses of carbon bricks. Thus, using a condenser of this type it is possible to maintain a temperature at the bottom of the condenser in the range of from about 2500 to 3500 F., such as about 3000 F. The temperature at the top of the condenser is thus maintained in the range from about 1250 to 1500 F., such as about l400 F.

What is claimed is:

1. Improved condenser assembly for condensing metallic vapors whereby contact between metallic vapors and the bare metal wall of said assembly is avoided which comprises, (l) means for introducing metallic vapors into said assembly, (2) means for withdrawing condensed vapors from said assembly, said assembly characterized by (3) having a metallic shell, and (4) containing a liner therein extending throughout said condenser assembly, said liner being characterized by having a relatively high heat transfer rate at the point of introduction of said metallic vapors and a relatively low heat transfer rate at the other end of said liner, the heat transfer rate progressively changing throughout said assembly, said liner being further characterized by consisting of different materials having different heat transfer rates, which materials are adjusted with respect to one another so as to secure a progressive heat transfer rate change.

2. Condenser assembly as defined by claim 1 wherein the heat transfer rate is progressively changed throughout said assembly by interchanging carbon bricks having a relatively low heat transfer rate for graphite bricks having a relatively high heat transfer rate in the respective courses of said liner.

3. Improved condenser assembly for condensing metallic vapors whereby contact between metallic vapors and the bare metal wall of said assembly is avoided which comprises, (1) means for introducing metallic vapors into one end of said assembly, (2) means for withdrawing condensed vapors from the other end of said assembly, said assembly characterized by having a (3) metallic shell and containing a liner therein extending from said one end to said other end, said assembly being further characterized by said lining having a relatively high heat transfer rate at said one end and a relatively low heat transfer rate at said other end, the heat transfer rate progressively changing throughout said assembly, said liner being further characterized by consisting of different materials having different heat transfer rates, which ma- 5 6 terials are adjusted with respect to one another so as to References Cited secure a progressive heat transfer rate change.

4. Assembly as detined by claim 3 wherein said liner UNITED STATES PATENTS at near said one end comprises a plurality of courses of 312401590 8/1962 Schmldt et al- 266-'34 X carbon bricks having a relatively low heat transfer rate and said liner at near said other end comprises a plu- 5 J' SPENCER OVERHOLSER Pnmary Exammer rality of courses of graphite bricks having a relatively J. E. ROETHEL, Assistant Examiner high heat transfer rate and wherein said liner between said one end and said other end comprises courses of U-S- Cl- X.R

carbon and graphite bricks. 10 203-86; 266-43 

